1. Field of the Invention
The present invention relates to apparatus for removal of a carrier film from the bottom surface of semiconductor dice and other electronic devices. Particularly, the apparatus of the present invention reduces the surface area of the adhesive film which remains in contact with a die during removal. The present invention also relates to a method for removing semiconductor dice and other electronic devices from carrier film.
2. Background of Related Art
Several apparatus and methods are known for removing semiconductors and other electronic devices from adhesive carriers such as film. Some such methods involve degrading the adhesive properties of the carrier. Some devices employ needles, pistons, or other mechanisms which apply an upward force to push the die off of the carrier. Other devices utilize a vacuum to pull a die from a carrier. Many known apparatus and methods for removing a die from a carrier cause damage to a significant quantity of dice.
U.S. Pat. No. 4,778,326, issued in the names of Althouse et al., discloses a method and apparatus for transporting semiconductor dice which is commonly referred to as a xe2x80x9cgel packxe2x80x9d or xe2x80x9cdie-pac.xe2x80x9d The semiconductor dice are loaded onto and adhere to a flat, thin, flexible silicone film, which is attached to a carrier base. The carrier base has recesses formed therein, into which the silicone film may be pulled as a vacuum is applied beneath the film. As the film is pulled into the recesses, the area of the silicone film which contacts the dice is reduced, thereby reducing the magnitude of the adherence by which the dice are attached to the film. The dice may then be easily removed with a vacuum tip.
As mentioned above, the predominant use of gel packs is to transport dice. No semiconductor fabrication processes are performed while dice are on a gel pack. Use of gel packs is somewhat undesirable because the silicone of the films tends to contaminate dice by leaving a silicone residue thereon.
U.S. Pat. No. 5,590,787, issued in the name of Hodges, discloses another die-pac device for transporting semiconductor dice. The device of the ""787 patent includes a UV sensitive adhesive and permits the penetration of electromagnetic radiation, such as ultraviolet light, therethrough.
Techniques which utilize carrier films having ultraviolet light (UV) degradable adhesives thereon or other degradable adhesives are also well known in the art. The area of film attached to a die which has been selected for further manufacture is irradiated with the appropriate degradative source to remove the die from the film. Although the use of UV radiation and similar methods are desirable from the standpoint that they are unlikely to damage the die, the adhesives and carrier films required for such devices and processes are very expensive. UV-release carrier tapes have also been employed to a limited extent with gallium arsenide dice.
U.S. Pat. Nos. 4,990,051 and 4,850,780, each of which issued in the names of Safabakhsh et al., each describe an apparatus for removing a die from an adhesive carrier film. That apparatus concurrently applies a vacuum to the exposed surface of the die and a chuck to the film on the opposite surface of the die. The vacuum collet is moved away from the chuck, which facilitates a pre-peel of a small area of the film from the periphery of the die. A piston disposed coaxially within the chuck is then forced against the carrier film to stretch the film and further reduce the area of the film which adheres to the die, thereby facilitating removal of the die from the film.
Some other apparatus for removing dice from a carrier film include a plunge-up piston which has a cap thereon to raise a selected die in relation to the adjacent dice on the film. This process is referred to as xe2x80x9ctentingxe2x80x9d the film. A needle disposed within the cap is actuated to contact the die from below and push it from the carrier film as a vacuum tip positioned above the die pulls the selected die away from the film.
Such tenting processes for removing dice from film are undesirable for several reasons. First, tenting sometimes creates an air bubble under the die, which tends to tilt the die, preventing the vacuum tip from obtaining a good hold on the die. In such cases, the vacuum tip will likely drop the selected die, damaging and/or contaminating the die. Second, in many such apparatus, the needles which push the selected die from the film have pointed ends, which tend to score the bottom surface of the die. Dice which have been scored in such a manner tend to subsequently fail mechanically at the location where they have been scored. Third, as the film is tented, the edges of other dice which are adjacent to the selected die may be chipped, causing damage to the circuitry on their active surfaces, with consequential failure.
U.S. Pat. No. 4,915,565, issued in the names of Bond et al., discloses an apparatus for removing a selected die from a wafer having an array of dice which is attached to a carrier film. In the apparatus of the ""565 patent, the dice are positioned beneath the film during removal of each selected die. A head having an array of needles protruding therefrom is positioned over the film opposite a selected die. In operation, the head plunges toward the film, the needles penetrating the carrier film and dislodging the die from the film. The dislodged die then falls into a receptacle. U.S. Pat. No. 4,759,675, issued in the names of Bond et al., discloses the same die removal device.
The sole use of needles to remove a selected die from a carrier film makes the removal device of the ""565 and ""675 patents undesirable. The adhesive forces of the film to the die necessitate a large amount of force for removing the die therefrom. Further, the orientation of the plunge head relative to the die requires that the die suffer some impact when falling into a receptacle, increasing the likelihood of damage to the die.
U.S. Pat. No. 4,285,433, issued in the names of Garrett, Sr. et al., describes another method and apparatus for selecting and removing singulated dice from a wafer. The apparatus includes an adhesive film which is attached to the bottom of the carrier film supporting the dice. The adhesive film with adhered carrier film is pulled away from the dice through a slot. U.S. Pat. No. 4,607,744, issued in the name of Pak, discloses a similar method and device which removes carrier film from dice with a take-up drum which pulls a free end of the carrier film. The carrier film is pulled around a separator edge into a slot, the dice then passing over the separator edge and onto a conveyer which transports the dice away from the separator edge.
The amount of force applied to the dice as the carrier film is pulled downward through such a slot or separator edge while the dice proceed in a different direction of travel may be sufficient to break or damage the dice. Further, the processes of the ""433 and ""744 patents are undesirable in that they do not permit automated removal of selected dice from an array of dice including failed dice and die fragments, as well as functional dice.
As dice become thinner and are fabricated with larger surface areas (which adhere to a greater area of the carrier film), the likelihood of their being damaged by each of the foregoing mechanical removal processes increases.
Thus, an apparatus is needed for removing disposable carrier tape or film from semiconductor dice and other electronic devices which exerts little or no impact on a die, reduces the area of carrier tape or film adhered to a die before removal of the die, and utilizes an inexpensive yet effective carrier tape or film.
In contrast to the deficiencies exhibited by the prior art, the low-stress die removal system of the present invention addresses each of the foregoing needs. The apparatus is useful with many disposable carrier tapes or films known and used in the art. The apparatus also exerts little, if any, impact on the die. The apparatus of the present invention also significantly reduces the surface area of carrier film adhered to a die before removal. The die removal apparatus does not require the use of expensive films which have degradable adhesives thereon.
One embodiment of the die removal apparatus of the present invention includes a base, including a plate member encircled by a raised periphery, a screen disposed over the plate member, and a vacuum source to create a vacuum within the base and below the screen. The plate member may include recesses therein to ensure application of the vacuum to all portions of the base within the periphery. A carrier film having dice on the upper surface thereof is placed above the plate, and the vacuum used to pull the film against the screen and away from the dice.
In a variation of the die removal apparatus of the present invention, the plate member includes a series of laterally-spaced supports protruding upwardly therefrom. The portions of the screen which overlay the supports may be higher than those portions which rest within the recesses. Another variation of the base of the die removal apparatus of the present invention lacks a screen and merely employs supports. Alternatively, a plate member may be formed with apertures therethrough and the film is pulled thereagainst and within the apertures upon activation of the vacuum source. In yet another variation, the upper face of the plate is provided with bumps, convolutions, or other protuberances separated by valleys into which the carrier film may be pulled.
In use, a frame ring which engages a carrier film with a wafer thereon is positioned over the base. The film preferably rests upon and is supported by the plate member. As the vacuum source is activated, the portions of the carrier film which overlay the recesses are pulled against the screen, supports, or protuberances and into the recesses or valleys. Thus, the area of the film which remains adhered to the dice is reduced by an amount which depends upon the size of the recesses and the strength of the vacuum. Consequently, the adherence of each of the dice to the carrier film is reduced. Dice which have been selected for further processing (referred to individually as a xe2x80x9cselected diexe2x80x9d) are then completely separated from the carrier film by a removal mechanism, which removes each selected die by pushing, pulling, or pushing and pulling each selected die from the film. Preferably, separation occurs while the film is being pulled downward against the plate member.
The die removal apparatus according to the present invention may also include a vacuum head which is positionable above a selected die. The vacuum head pulls the die from the carrier film upon activation of a vacuum source to pull a substantial portion of the film away from the back side of the die. When combined with the significantly reduced adhesion area of the film to the die, very little force is required to remove the die from the carrier film. Further, because the die rests securely upon and remains supported by the plate member, tilting of the die is unlikely.
The die removal apparatus may also comprise a low-impact plunge-up head which is positionable beneath a selected die and has one or more needles which may be extended upwardly therefrom in a telescoping manner. After the plunge-up head is positioned beneath the selected die, the needle is actuated to push the die away from the carrier film. When combined with the significantly reduced adhesion area of the film to the die, afforded by the previously-mentioned base construction and application of vacuum to the back side of the film, very little force is required to remove the die from the carrier film. Preferably, the plunge-up head is used in combination with a vacuum head which is positionable above the selected die. Preferably, when used in combination, as the plunge-up head needle pushes the die upward, the vacuum head simultaneously lifts the die to transfer it to another location. As with the first embodiment of the removal mechanism, the likelihood of damaging a selected die is much less than that of methods which were previously known in the art.
Other advantages of the present invention will become apparent to those of ordinary skill in the art through a consideration of the appended drawings and the ensuing description.